It is estimated that more than a million joint replacement surgeries are performed each year worldwide. It is further estimated that that number will double in the next ten or twenty years. While joint replacement surgeries are common and generally very successful, they are not without risk. Frequent complications include loosening of the implant, infection and deep vein thrombosis (DVT).
DVT affects millions of people each year. DVT occurs when blood cells coagulate within a deep vein. Once a DVT occurs, portions of the clot can break free and move through the bloodstream to the lungs or brain. A clot that lodges in the lungs may block blood flow within the lungs, causing a potentially fatal pulmonary embolism. A blood clot that reaches the brain may cause a stroke. As many as 200,000 people die each year as the result of complications from DVT.
A post-operative joint replacement patient is at the highest risk of developing a DVT approximately ten to twelve days after surgery. At that point, the large majority of patients are being cared for on an outpatient basis. To prevent the formation of DVT, and avoid the risks associated with DVT, doctors generally prescribe one or more forms of DVT prophylaxis, which include primarily chemical and mechanical DVT prophylactic therapies. While each of these therapies is beneficial in some respect, each suffers significant shortcomings.
Common types of chemical DVT prophylaxis include drugs such as warfarin and heparin, which are used to prevent the patient's blood cells from adhering and forming clots. These drugs work by effectively preventing the formation of certain proteins that are needed for blood to clot. While they are effective, they are also very dangerous. The treatment leaves patients at high risk for various potentially fatal bleeding problems including, but not limited to, gastrointestinal bleeding and brain hemorrhage. Further, a number of patients are advised not to use anticoagulants due to various other conditions that create increased risk of fatality. Hence, there is a need for effective non-chemical DVT prophylaxis.
The most common mechanical DVT prophylactic therapy, device is a pneumatic sleeve, which consists primarily of a flexible plastic envelope that encloses a portion of a limb—generally a lower limb. The envelope is periodically inflated to create pressure against the tissues of the limb. The periodic compression and release of the tissues serves to facilitate blood and fluid exchange. When the pneumatic pressure within the envelope increases, the tissues are compressed and a portion of blood and other fluids in the limb are forced out through the circulatory and lymphatic pathways. When the envelope is deflated the limb is free to fill with fluid unimpeded. This method of providing mechanical compression increases the overall velocity of venous flow. Additional means of providing mechanical compression include stockings, compression straps, massage and vibrations, each of which is also designed to increase circulation and fluid exchange.
Mechanical DVT prophylaxis is beneficial in that it physically aides movement of blood and other fluids. Additionally, it is believed to have a wider systemic effect, likely due to the release of various anti-clotting factors during endothelial compression. However, existing means of mechanical compression are enormously imperfect. Circulation in the lower limbs is predicated on the function of one-way valves in the large veins. Currently used devices, such as compression stockings and pneumatic sleeves, attempt to cause movement of fluid in the limb by creating non-directional mechanical compression of the tissues. However, because this compression is non-directional, it simply creates pressure against which blood must be pumped on its way from the distal end of the extremity back towards the torso. This type of non-directional mechanical compression is very inefficient. Accordingly, there is a need for a device that causes directional mechanical compression of the lower limb, oriented such that the compression pushes blood up the limb and back towards the heart, effectively aiding the one-way valves of the leg.
In addition to being an inferior method for increasing venous flow, existing methods of providing mechanical DVT prophylaxis are cumbersome and difficult to maneuver. For example, pneumatic compression sleeves consist of various fasteners, tubes, electrical cords and a machine. Post-operative patients are generally taking significant pain medications, experiencing very limited mobility, and are often elderly. The equipment for providing mechanical DVT prophylaxis creates an additional hazard for these patients, and as such, doctors hesitate to send patients home with such a device. Accordingly, patients often do not receive adequate DVT prophylaxis during the critical ten to twelve day period. Hence, there is an additional need for a system that is simple and portable such that it is practical for use both in a treatment facility and at home.
In addition to preventing formation of DVT and other risks associated with joint replacement, doctors generally prescribe a physical therapy regimen to aide the patient's functional recovery.
Continuous passive motion (CPM) machines are used regularly in orthopedics and physical therapy. These machines are most often used after surgical procedures, such as joint replacement. The machine moves a patient's limb through a predetermined range of motion without physical exertion by the patient. The passive movement of the affected limb has several positive effects. First, CPM helps to prevent the adhesion of superficial tissues to deeper tissues during healing. These adhesions, if developed, can limit the range of motion of the joint and therefore limit the functional recovery of the patient. Second, CPM serves to stretch the tissues around the joint to maximize flexibility and prevent healing of tissues with stiff fibrous connections that further limit mobility.
Often, when a post-operative joint replacement patient is discharged from the hospital, the doctor prescribes a CPM regimen, to be performed on an outpatient basis. A CPM machine is generally purchased or rented from one of a variety of companies. Medicare covers the cost of renting a CPM machine for the prescribed period of time following some joint replacement surgeries.
In view of the foregoing, there is a need to provide a more effective system for providing mechanical DVT prophylaxis, both within the treatment facility and at home, particularly ten to twelve days after surgery. An ideal device would be portable and simple to use such that it can be used safely on an outpatient basis. The system should provide directional compression such that it effectively aides movement of the blood from a distal position back towards the heart. Further, the mechanical DVT prophylactic therapy is preferably provided in combination with CPM therapy because the simultaneous provision of CPM and mechanical DVT prophylaxis is likely to provide enhanced synergistic effects such as enhanced venous flow during CPM that likely serves to further reduce the risk of DVT formation, and increased blood supply to the damaged tissue during DVT prophylaxis that may serve to increase the rate of healing and enhance the ability to fight infection. Finally, the therapies are ideally provided in combination because such an arrangement is cost effective for the large number of patients on Medicare. The present invention addresses one or more of these needs.